The invention concerns a fluid guideline with at least two structural elements made of substantially soundproof material and at least one opening for noise damping, whereby an impedance change (in particular in the form of an impedance discontinuity) of the flow resistance of the fluid flowing through the fluid guideline is present between two adjacent structural elements.
In tubes for untreated air that are installed in engine compartments of motor vehicles in order to take up or, respectively, to guide surrounding air from the radiator to an air filter, one makes an effort on the production side to reduce the prevalent sound level during the motor operation. In the automobile industry, for this purpose one follows primarily two methods. Either resonators are attached to the tubes for untreated air, or tubes for untreated air are equipped with what is known as a bypass tube, whereby specific frequencies can be filtered out. Technically refined resonators should filter out as broad a spectrum of noise as possible and can be detuned, while bypass paths can optionally be connected or, respectively, separated by valve controls. However, resonators require some space (in places they comprise a volume of some liters) and bypass tubes also increase the amount of material due to a length of up to 30 cm. In the continuous search for simple and effective noise-reducing tubes for untreated air, the use of porous materials in the processing of untreated air is also under discussion.
Thus, from JP 60050265, a sintered, porous pipe socket made of aluminum powder is known that is connected via a tube piece with an air filter. The porous, permeable pipe socket thereby characterizes itself by a substantially reduced sound level with consistent air supply efficiency. However, the pipe socket has the disadvantage of higher material costs.
EP 0 837 238 A2 discloses the use of a porous, malleable, sound-absorbing material with which the air filter or its supply line can be lined internally. An additionally lined inner wall likewise leads to an increased expenditure of additional costs.
The use of a porous band material to produce a tube is known from EP 818 648 B1. A band is thereby coiled in the shape of a tube as well as glued in the form of a tube and used for sound damping in the air tube in the engine compartment. In practice, a woven synthetic is used as a porous material, whereby in addition to the actual shaping treatment process, the production of the woven band is additionally expensive.
Openings for noise damping used with impedance changes are known in the prior art. Thus, for example, a line section is known from WO 00/45044 that is assembled from two shells connected with one another, whereby gaps are arranged in the interstices between the shells for damping. In addition, the line section exhibits a diffuser effect and the tube wall can be provided with bores. Overall, the known line section is very complex in assembly.
According to DE 196 29 368 A1, a constriction reducing the diameter of a tube is provided at a perforation of the tubes to suppress the generation of harmonic tones by sound damping for pulsing gases, in particular for exhaust gas from internal combustion engines, with separation from the perforation. This leads to a relatively complicated assembly.
A fluid guideline according to species is known from GB 2 364 352. In the known fluid guideline, straight, stiff elements are perforated with openings and respectively arranged between flexible elements, whereby the flexible elements can be fashioned as a type of corrugated tube section. The introduction of openings in the straight elements must thereby ensue in adaptation with the geometry of aforesaid elements (which is relatively time-consuming and expensive) in order to generate a desired sound damping.